1. Field of the Invention
This invention relates to an image processor capable of displaying a plurality of color images.
2. Description of the Prior Art
Recently, bit map type color displays having a multi-window system capable of handling a plurality of application software programs on the same display screen have popularly been used as display units of information processing systems such as work stations or personal computers.
The color of each dot (pixel) of such bit map color displays is controlled based on a color map consisting of a table such as that shown in FIG. 6, which has pixel values (fixed numbers) and values r (red), g (green), and b (blue) and in which the appropriate values r, g, and b are obtained if a corresponding pixel value is given. For example, an 8-bit-plane in bit map display has a color map having 256 (=2.sup.8) entries and is capable of simultaneously displaying 256 colors at the maximum by using pixel values from 0 to 255, inclusive. These 256 colors are determined by arbitrary combinations of values r, g, and b. For example, if the values r, g, and b are each 8-bit, an arbitrary set of 256 colors can be selected from 2.sup.8 .times.2.sup.8 .times.2.sup.8 colors.
In a case where a certain application requires 64 colors for display, 64 entries are provided from 256 entries of the color map, and the values r, g, and b of each entry are set.
Conventionally, the provision of a color map and the setting of values r, g, and b and so on are effected separately and independently by the applications using the corresponding color map entries.
For this reason, in a case where a plurality of application programs run simultaneously to effect display through separate windows, each application independently prepares a color map, and the color map resources are soon exhausted. If in this state another application tries to run,
(1) it cannot run because the desired color map cannot be provided, or PA1 (2) it is started by finding entries close to the values r, g, and b which are to be set among the color map entries already maintained and by setting the system so as to use such entries.
For image display, however, one color map is frequently used to form a plurality of images, and it is ordinarily necessary to suitably maintain the accuracy of values r, g, and b set in color maps.
In the case of a method in which (1) is true, the number of applications which can display images simultaneously is small. For example, an 8-bit-plane display unit can simultaneously display 256 colors. However, if several applications each requiring 64 display colors are running, it allows only 256/64=4 applications to be activated irrespective of whether or not some of the applications use a color map having the same values r, g, and b. That is, the number of applications which can run simultaneously is limited because no color map can be used in common for two applications.
In the case of a method in which (2) is true, if among color map entries already provided there are entries of the same values as the values r, g, and b which are to be set for the new application, and if such entries are found, the system can be set to use those entries and to effect display with the accurate values r, g, and b. However, if the number of color map entries to be set is large, it is necessary to search the previously-set color map entries one by one, and the time needed for this operation is long.
Also, in this case, it is possible that, depending upon the searching method, color maps will be assigned respectively to two applications requiring the same color map. This method also entails the problem of limitation of the number of applications which can run simultaneously, since the color maps are not effectively assigned.
The above-described problems are owing to failure to enable a plurality of applications to effectively hold color maps in common.